1. Field of the Invention
The present invention generally relates to a railway or railroad track and, more particularly, to an improved insulating plate employed for a rail having an insulated joint in order to achieve an electrical insulation of a track circuit.
2. Description of the Prior Art
Conventionally, for rails having insulated joints of the type referred to above, there has been provided the so-called ordinary insulated rail in which insulating plates are disposed between the rail and joint plates. Also, there has been provided a glued insulated rail in which a bonding agent is filled between the rail and the joint plates. The former ordinary insulated rail has such a disadvantage that the insulating plates tend to be quickly deteriorated, thus resulting in an insufficient stability of the track as a whole.
More specifically, in FIG. 1, there is shown a joint portion J of a conventional ordinary insulated rail, with an insulating plate 2 thereof illustrated on an enlarged scale in FIG. 2. In FIG. 1, the rail joint portion J includes the pair of insulating plates 2 each formed with bolt inserting through-holes 3 (FIG. 2), and a corresponding pair of joint plates 4, so that a rail 1 is held, at its opposite sides, between the joint plates 4 through the insulating plates 2 which are clamped together by bolts 5 extended through the holes 3 of the insulating plates 2 and nuts 6 engaged with the bolts 5 so as to constitute the joint portion J.
Each of the insulating plates 2 made of a resin such as polyamide or the like is molded to have a generally U-shaped cross section for close contact with the side face of the rail 1, while each of the joint plates 4 prepared, for example, by forging is poor in the surface finishing accuracy, with its surface not being necessarily in conformity with the corresponding side face of the rail 1, and thus, the joint plates 4 locally contact the insulating plates 2. Since the joint plates 4 and the insulating plates 2 under such a state are forcibly clamped together by the bolts 5 and the nuts 6, strong forces are applied to the locally contacting portions due to loads, impacts, etc. during passage of trains, and consequently, the insulating plates 2 may be damaged in a short period. Moreover, even when the same insulating plates 2 are employed for a plurality of joints J, there is a difference in the degree of deterioration owing to the difference in the manner of contact between the joint plates 4 and the insulating plates 2, resulting in an inconvenience from the viewpoint of maintenance.